The present invention relates to a control system for an area covered by base stations and, more particularly, to a base station coverage area control system in a mobile communication system.
According to EIA (ELECTRIC INDUSTRIES ASSOCIATION) IS-3-D or TACS (TOTAL ACCESS COMMUNICATION SYSTEM) Issue-4 as specifications of a cellular mobile radio communication system, a plurality of base stations are arranged in a service area. Each base station has at least one communication channel, and communication between mobile stations and the respective base stations is performed by using the communication channels.
In order to increase the system capacity, the technique of frequency reuse is employed. In this technique, the same frequency is used by different base stations to increase the number of communication channels simultaneously used in the service area under the condition that signals transmitted from the respective base stations do not interfere with each other.
In this case, an installation plan of base stations is made in consideration of estimated system capacity, distribution of subscribers, and radio wave propagation characteristics in the service area (Okumura, et al., "Experimental Study of Propagation Characteristics in Land Mobile Radio Communication" Kenjitsuho, Vol. 16, No. 9, pp. 1705-1764, 1967). After this consideration, the following adjustment operations are performed: adjustment of the transmission output of each base station, adjustment of the horizontal directivity by using an omnidirectional antenna or a fan-beam antenna, and adjustment of the range by changing the directivity of an antenna in a horizontal or downward direction.
The respective adjustment operations described above, however, are performed at one point where a base station antenna exists. For this reason, if a local dead area due to a building or the like is present, the coverage areas of adjacent base stations using the same frequency are adversely affected to expand the dead area.
In addition, if the traffic intensity is locally increased as a function of time, proper distribution of communication channels between base stations is difficult to realize.